Chemical vapor deposition (CVD) systems are used to form a thin, uniform layer or film on a substrate such as a semiconductor wafer. During CVD processing, the substrate is exposed to one or more chemical vapors such as silane, phosphane, diborane and the like, and gaseous substances such as oxygen. The gases mix and interact with the other gases and/or the surface of the substrate to produce the desired film. The desired reactions generally occur at elevated temperatures, for example 300.degree. C. to 500.degree. C., with the substrate and chamber being heated to the appropriate temperature for a selected process. In many applications including semiconductor processing, film characteristics such as purity and thickness uniformity must meet high quality standards.
In general, CVD systems include an injector positioned to inject chemical reagents and other gaseous substances into a clean, isolated reaction chamber. For processing occurring at atmospheric pressure, the substrate, for example a thin glass substrate, is often carried through one or more chambers on a conveyor. As the substrate travels toward the processing chamber, the substrate and the conveyor carrying the substrate are heated by heaters positioned adjacent to the conveyor as the conveyor and substrates move together toward the processing chambers. To heat the substrate and conveyor to the desired temperatures without damaging the substrate, the conveyor typically moves the substrate along a heating path having a length of about six feet before the substrate reaches the first reaction chamber. After processing, the substrate is carried along a cooling path of a similar length, requiring that the CVD system occupy about twelve feet solely for heating and cooling the substrate before and after processing. A thermal conditioning system requiring a smaller footprint to heat and cool the substrate would reduce the size of the overall system, allowing the system to be operated in a smaller area. Heating the substrate as it is carried by the conveyor heats the leading edge of the substrate first, producing a thermal gradient in the substrate during the heating process. This thermal gradient may have adverse effects on the substrate or materials previously deposited on the substrate. A heating system which uniformly heats the substrate is desirable. Similarly, a system which thermally conditions the conveyor before a substrate is deposited on the conveyor is desirable. A system in which the heated substrate is transferred to the heated conveyor in a heated and contaminant free compartment is also desirable.